The technical scope of the invention is that of devices, and notably projectiles, able to trigger an avalanche.
It is known to artificially trigger avalanches, this in order to prevent too great an accumulation of snow in an avalanche corridor thereby reducing the risks to the buildings and persons located on the lower part of the slope.
Known devices enabling avalanches to be triggered are either fixed or mobile.
Fixed installations are costly. Indeed, the infrastructure are generally built in places that are difficult to reach, and they also require electrical or fluid (combustible gas) connections, which are difficult to ensure.
Thus, patent FR-2771168 describes an avalanching device that pumps up balloons using an explosive gas.
Patent FR-2636729 proposes the permanent installation of an explosive gas generating ramp oriented towards the slope.
Other devices more often than not implement a compressed air gun that launches an explosive projectile triggered by an impact fuse. U.S. Pat. No. 5,872,326 describes such a projectile.
These devices also have drawbacks.
Thus, the conditions of use are limited by the safety of the explosives being implemented (transport, storage, loading). Moreover, in the event of a malfunction, an explosive projectile risks being present on the ground, thereby posing a risk to safety and the environment.
Up to now, these risks have been attenuated through the use of dual component explosives. Two components are mixed in the projectile body in-situ before firing. Individually the components are inoffensive thereby ensuring their safe transportation and storage. The mixture is explosive but becomes inert after a period of 48 hours thereby eliminating risks linked to the abandonment in situ of non-ignited projectiles.
However, the projectiles are difficult to implement since they require the components to be mixed together in situ. This operation is made difficult by the climatic conditions (cold, damp) and the topography of the terrain (hilly). Thus, in practical terms, known projectiles are either fired from a fixed platform, or brought vertically by helicopter in the vicinity of the avalanche corridor. Once again, implementation is both complicated and costly.
A further drawback lies in the event of the inadvertent suspension of fire for whatever reason (bad weather, launcher breakdown . . . ). If the explosive mixture has been made and firing is not possible, then the live projectile has to be kept in storage for 48 hours.
The aim of the invention is to propose a projectile to trigger avalanches that overcomes such drawbacks.
Thus, the projectile according to the invention is simple to implement since it does not require an explosive mixture to be prepared in situ. It may be easily implemented whatever the terrain and notably using light launchers that can be brought by trackers.
It offers an excellent level of safety, both before and after firing, in the event of a triggering failure.
Thus, the invention relates to a projectile to trigger avalanches and intended to be projected by a launcher tube, such projectile comprising a casing intended to explode in the vicinity of or in contact with the snow through the action of priming means in order to cause an avalanche, wherein said casing is able to be pressurized during firing and/or during its trajectory, the pressurization of said casing thus obtained being insufficient by itself to ensure the exploding of the casing, other means being provided to overpressure the casing thereby ensuring its exploding.
The pressurisation of the casing during firing may be obtained by using part of the propellant gases, inside the launcher tube, used to fire the projectile.
The casing may be pressurized during firing and/or during trajectory by means of first gas-generating means integral with the projectile and ignited during firing.
According to a first embodiment, the projectile comprises a piston pushed by the gas pressure supplied by the launcher or by the first gas generator and allowing the gases to enter the casing, such piston being brought back into a closing position by a return spring and ensuring the gas pressure is maintained inside the casing.
This projectile will also comprise a second gas generator activated by priming means enabling an overpressure of the casing to be ensured causing it to fracture.
Advantageously, the gas pressure generated by the second generator will not be enough to ensure the fracturing of the casing on its own.
The second gas generator may comprise a pyrotechnic composition or a powder charge ignited by priming means.
The priming means may comprise a percussive fuse to ignite the second gas generator when the projectile impacts on the ground.
The projectile may comprise a combustion monitoring device for the pyrotechnic composition or the powder charge.
According to a second embodiment, the second gas generator may ensure the generation of a combustible and/or explosive gas that will be ignited upon impact by priming means.
The second gas generator may comprise calcium carbide that will be mixed with water during the trajectory, the water being contained in a reservoir that will be opened by opening means activated during firing.
The opening means may comprise a riser head able to translate against the action of a return spring, such riser head being pushed towards the reservoir through the inertial force deployed during firing, thereby ensuring the fracturing of the reservoir.
The priming means may comprise a percussive primer placed at a front part of the projectile and ignited by a percussion device.
According to a third embodiment, the first gas generator may ensure the generation of a combustible and/or explosive gas.
The first gas generator may comprise calcium carbide that is mixed with water during the trajectory, the water being contained in a reservoir that will be opened by opening means activated during firing.
The opening means may comprise a piston sliding in the reservoir against the action of a return spring, the piston being displaced during firing through the action of the propellant gases and carrying a pin allowing the reservoir to be pierced thereby ensuring that the water and calcium carbide come into contact with one another.
The calcium carbide may be placed in a spray tube perforated with radial holes, such tube being coaxial to the projectile and placed in the prolongation of the reservoir.
According to one variant, the return spring may be made of a shape-memory material selected and parametered such that it retracts when it reaches a temperature beneath a certain rate and thus no longer exerts the same return force on the piston.
The priming means may comprise a percussive primer placed at a front part of the projectile and ignited by a percussion device.
The priming means may comprise at least one detonating cord placed on an internal surface of the casing.
In any event, the priming means may comprise a primer connected to delay means ignited during firing.
The projectile may comprise a controlled leak device ensuring the gradual depressurisation of the casing.
The controlled leak device may comprise at least one interior cap made of a porous material.